Process for recovery of aromatics



Jan. 31, 1956 G. P. HAMNER PROCESS FOR RECOVERY OF' AROMA'I'ICS SEPARATED FROM CYCLIC DIENES Filed Sept. 7, 1951 ,mwiw/ ...v LW@ Erm/enter' d uoa :Yu @who United States Patent O PROCESS FOR RECOVERY F AROMATICS SEPARATED FROM CYCLIC DIENES Glen P. Hamner, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware Thev present invention has to do with recovery of aromatic fractions suitable for preparation of pure benzene and pure toluene with separation of interpolyrnerized dioletins therefrom following segregation of valuable C diolenic components.

Hydrocarbon streams from high-temperature vaporphase cracking of petroleum contain largely oletms, dioletins, and aromatic hydrocarbons with relatively small amount of paraltins.

In addition to cyclopentadiene and methyl cyclopentadiene there are other cyclic diolens and conjugated openchain diolens of higher molecular Weight which tend to distill together with benzene and toluene from the hydrocarbon streams containing these compounds, despite various efforts to remove the diolelins by simple or drastic steps from a narrow boiling fraction of the high-tempera.ure vapor-phase cracked petroleum products.

The high-temperature vapor-phase cracking processes have already been described in the prior art and need not be more fully discussed. In these high temperature cracking processes, naphtha through gas oil boiling range petroleum, fractions, boiling in the range of 250 to 700 F., are cracked in the vapor phase at 1000 F. to 1600" F. in a short period of about l to 5 seconds under low pressures of about l to l0 atmospheres, and in the presence of steam amounting to about 50 to 90 mole per cent based on the hydrocarbon feed. A` process of this type is described in U. S. Patent 2,363,903, patented November 28, i944, by B. l. Smith, and U. S. Patent 2,348,659, patented May 9, 1944, by B. I. Smith et al.

rlhe patents relating to the vapor-phase cracking also describe certain methods of recovering low-boiling fractions up to and including a butadiene-containing fraction and recovering the higher fractions from the highly cracked products.

The present invention is concerned more particularly with recovery of other individual valuable higher-boiling C5 to C'z compounds and polymer products in an etlicient manner. These higher-boiling valuable hydrocarbons include such substances as isoprene, cyclopentadiene, methyl cyclopentadiene, benzene, and toluene mixed with Cs-ldioletins, dimethyl cyclopentadiene, ethyl cyclopentadiene, and desired polymers of thedioletns.

It has been found in reducing the present invention to practice that for improved recovery of each of the individual types of products, certain precautions have to be taken during the separation steps to prevent undesired polymerization reactions and decomposition reactions while segregating the various components, otherwise the recovery of the desired iinal substances in high purity and good yield is adversely affected.

According to the present invention, final benzene and toluene concentrates suitable for purification, for example, by known methods of extractive distillation, are obtained from two or more separately processed cracked distillate streams: the first or lightest stream being richest in Cs-Cs hydrocarbons, the second or intermediate b oiling range stream being richest in C'i-l- (C7 and higher) Patented Jan. 31, 1956 hydrocarbons, and a third stream is richest in Ca+ (Ca and higher) hydrocarbons. The separate treatment of each of such streams from a high temperature vapor phase cracking process will be discussed in greater detail with reference to the ow plan of the accompanying drawing.

(l) The Cs-Ce rich stream.-This stream contains 20-25 weight percent C5, 40-50 Weight percent Cs, and 25-25 weight percent C7 hydrocarbons with some dimerized C5Cs cyclo-dienes and negligible amounts of C4 hydrocarbons.

Referring to the ow plan in the drawing, the Cs-Cs rich fraction passed as the lightest stream through line 1 is first thermally soaked at a temperature of 200-220 F. for 4 to 8 hours in a soaking zone S-1 for selective and practically complete dimerization of cyclopentadiene and methyl cyclopentadiene present in such a fraction. The dimerization selectivity approaches when the suitable conditions of the order mentioned are used for selectively dimerizing the Cs-Cs cyclodienes without polymerizing other dioletns present in this fraction.

The dimerized C5-Cs rich fraction is fed from the soaking zone S-l through line 1A to a fractionating column A. An overhead fraction boiling in the range of about 60 F. to 300 F. is removed overhead from column A as a distillate stream through line 4. The Cs-Cs cyclodienes are recovered to the extent of 90-95% as dimers in the bottoms of column A and removed through line 5. The bottoms temperature of column A should not eX- ceed 280 F. to avoid undesired depolymerization of the dimers while separating the other type of hydrocarbons from the dimers. For optimum operation, pressures of 5 to l0 p. s. i. g. and temperatures from 185 F. to 260 or 240 F. are maintained from top to bottom in column A. t

The overhead distillate from column A contains Cs-C'z hydrocarbons from which about 15 weight percent of the feed to this column is obtained as the dimer bottoms product. The C5 hydrocarbons include 15-20 weight percent isoprene, 10-15 weight percent piperylene, 15-20 weight percent tertiary alkenes, 40-45 weight percent non-tertiary alkenes and less than 5% parains. The Cs hydrocarbons include 15-20 Weight percent dienes, l0-l5 weight percent tertiary alkenes, 40-45 weight percent benzene, 20-25 weight percent non-tertiary alkenes, and less than 3 Weight percent parains. The C7 hydrocarbons are similar to the Cs hydrocarbons in type and proportions except that toluene is 40-45 weight percent of the C1 components.

(2) C7+ rich stream.--This stream contains about 2 3 weight percent C5, 10-15 weight percent Cs, and 80-'85 Weight percent CH- With relatively minor amounts of higher hydrocarbons above C13. This stream is fed by line 2 to fractionating column B. An overhead distillate stream boiling up to 149 F. is removed by line 6 from column B and advantageously sent to the soaker S-l for separation of additional Cs-Cs components. An intermediate fraction of side stream boiling mainly in the range of 149-l85 F. is withdrawn through line 7 from column B. This intermediate fraction is close cut and contains about 45-50 weight percent benzene, 15-20 weight percent dienes including cyclodiene monomers since this fraction has not been thermally soaked, 10-15 weight percent tertiary alkenes, 15-20 weight percent non-tertiary alkenes, 5-10 weight percent cyclopentenes, and less than 3 weight percent parans. The bottoms or residual product of column B removed by line 8 is F. and higher-boiling material that need not be further treated for recovery of selected hydrocarbons. Pressures of l5 to 20 p. s. i. g. and a bottoms temperature of 350 F. are suitably maintained in column B.

(3) The Ca-lrich strewn-This stream contains approximately 20-25 weight percent C7 hydroc-arbons, and 70-80 weight percent Cs-lhydrocarbons including a minor amont of hydrocarbons heavier than C13. This stream is passed by line 3 to be fractionated in column C so that substantially all its toluene content is distilled overhead to be removed by line 9 as a C7 fraction boiling up to 250 F. The C7 overhead distillate stream contains 10-15 weight percent dienes, 40-45 weight percent toluene, and to 10 weight percent paraiins, the remainder being alkenes. The proportion of parafins may be higher depending upon the type of petroleum naphtha cracked to obtain this stream. The residue or bottoms fraction in tower C is the 270 F. and heavier material withdrawn by line tor use in motor gasoline or other purposes. Pressure of 85 to 90 p. s. i. g. and a bottoms temperature of 435 F. are suitably maintained in column C.

The distillate stream removed by line 4 from tower A is fed to fractionating column D. Column D is operated to take overhead a C5 fraction boiling up to l40 F. as stream 11 and to yield a bottoms Cs-C7 rich fraction, Since distillate streams 7 and 9 from towers B and C respectively are substantially Cia-free, they are then combined, as a stream 12, with the bottom Cs-C fraction withdrawn by line 13 from column D to form stream 14 which is fed to the second' thermal soaker S-Z. Pressures of l5 to 25 p. s. i. g. and a bottoms temperature of 260 F. are suitably maintained in column D.

The thermal soaker S-Z is a vessel in which the comd bined benzene and toluene rich fractions from the initial streams combined in line 1.3 are held under pressure at a more elevated soaking temperature than was used in the iirst soaking vessel S-ll, e. g., being held under pressures of 100 to 400 p. s. ig. at 220 F. to 400 F. for 6 to 8 hours. In this second soaker, Cs-lcyclodienes are polymerized and interpolymerized with open chain Cs-ldioletins, the olefinic hydrocarbons having 6 and more carbon atoms per molecule thus being more intensely polymerized.

The liquid containing the polymers formed in soaker S-Z is fed by line 15 into fractionating column E. Column E is operated to take overhead a distillate fraction boiling within the range of l40-240 F. through line 16. The polymers of the cyclodienes and straight chain dimers are removed as a bottoms stream 17 from column E. The bottoms temperature of column E should not exceed 280 F. and should preferably be closer to 240 F. to avoid depolymerization of unstable polymers. The

desired fractionation in column E may be accomplished with the aid of steam injected from line 1S or under vacuum. Pressures of 5 to 10 p. s. i. g. and temperatures in the range of 185 F. to 260 F. are suitably maintained in column E.

The overhead stream 1l from colunmn D is a C5 rich fraction suitable for recovery of isoprene by extractive distillation, a piperylene concentrate, and other C5 products. The recovery of these Cs products may be carried out with the use of known extractive processes, such as employ an aqueous acetone solvent.

The benzeneand toluene-rich distillate stream 16 taken overhead from column E is satisfactorily free of reactive dioletinic hydrocarbons that are undesirable sludge forming substances in subsequent extractive distillation treatments used for recovery of benzene and toluene of high purity, for example, cxtractive distillation with phenols, furfural, or triethylene glycol. Furthermore, by the separation steps used in obtaining the benzene and toluene distillate from column E there is very little loss of benzene or toluene from the amounts initially available in the initial crude cracked products.

A highly important advantage is gained through the use of the two separate polymerization operations that permit recovery of a valuable cyclopentadiene. dimer product (in stream 5 from column A), a good recovery of isoprene and piperylene in stream 11 from column D, and nally a removal of reactive diolenic hydrocarbons as a polymer product (in bottom stream 17 from column E).

Tests were conducted to determine the eiciency of the operation described for yielding benzene and toluene concentrates suitable for purification by extractive distillation with phenol. The results of these tests indicated that thermal soaking at elevated temperatures of a Cta-C7 stream is as ellicient as clay treatment at similar temperatures for removing sludge-forming diolens. In comparative tests, separate portions of the Cty-C7 fractions were treated at about 300 F. by thermal soaking as prescribed for zone S-2 and by clay. The treated materials were fractionated to obtain a 185-240 F. toluene fraction distilled away from the polymers and the toluene fractions were contacted with phenol under extractive distillation conditions of 350 F. for three hours.

Tests have demonstrated that polymers of the C5 and Cs cyclodienes and of some other dioletins close-boiling thereto are the polymers which are most susceptible to depolymerization under conditions of fractionally distilling the benzene and toluene concentrates; therefore, there is a certain advantage gained by eliminating the Cs and Cs cyclodienes by dimerization and eliminating Cs acyclic diolens by distillation from stream 1 in which they are mainly present before the combined distillation Cre-C7 rich fractions of the several streams are subjected to the higher temperature second stage polymerization to form more stable polymers from remaining Cta-C7 dioletins.

Attention is called to the fact that in the described process, only one of the initial streams need have all its components encounter' polymerization conditions in the tirst soaker S-1. The lowest boiling stream 1 which is richest in C5 and CG hydrocarbons first becomes subjected to the selective thermal polymerization in the polymerization vessel S-L Some of the components of this stream after removal of cyclodiene dimers in fractionator A and removal of C5 distillate from ractionator D are subjected to the non-selective polymerization in the second polymerization vessel S-Z. On the other hand, certain distillate fractions from the second and third streams that reach the second polymerization vessel S-2 need not bc subjected previously to a selective thermal polymerization (cyclodiene dimerization).

Since the polymerization which is effected in the second polymerization vessel S-2 is intended to be farreaching or more drastic in polymerizing as much of the acyclic Cfr-C7 diolens as possible atv elevated temper-atures, this non-selective. polymerization in S-Z may be carried out with the aid of polymerizing catalysts, such as activated or mineral acid treated clay, at temperatures of the order of 220 F. to 400 F. and under pressures suiciently high to maintain the hydrocarbons undergoing treatment in the liquid phase, e. g., to 400 p. s. 1. g.

Although the operations have been described in detail with regard to treatments of three initial separate streams; a Cs-Cs rich stream (l), a C7+ rich stream (2), and a C-lrich stream (3), an important factor of the operations involve the treatments of principally streams (l) and (2).

In the treatments of streams (l) and (2), it is particularly desirable. to avoid having a high concentration of diolens that are close-boiling to benzene, such as in stream (2), mixed with the material of stream 1) which is subjected to the selective polymerization or cyclic dioletin dimerization. in vessel S-l. It is beneficial for the quality of the dimer product withdrawn by line 5 from column A, for the separation of a suitable C5 cut withdrawn overhead from column D, and for the quality of. they polymer product withdrawn from column E by line 17,v if Cs and. higher diolelnicv hydrocarbons boiling above F. are diverted to the polymerization. zone tions of C5 and C5 components but its components should be mostly lower boiling than Cv hydrocarbons vfor improved separation of cyclic diolen dimers in column A following the thermal dimerization. The next higher boiling stream (2) thus will contain mostly hydrocarbons higher boiling than C'z hydrocarbons if separated from stream (l) by ordinary fractional distillation of a cracked naphtha.

What is claimed is:

l. In a process of separating C5 and Ce cyclic diolefns, C5 acyclic diolefins, benzene and heat stable polymers of diolens from vapor-phase cracked naphtha fractions containing C5 to Cr-lcyclic and acyclic diolens with benzene, the steps of thermally soaking a C5-Cs rich fraction to dimerize C5 and Ce cyclic dioletins therein, dstilling remaining unreacted C5 and Cs hydrocarbons from the dimerized cyclic diolefins, separating C5 acyclic dioletins from the resulting C5-Ce rich distillate which is distilled from the dimerized cyclic dioleins, subjecting the remaining C5 to Cs fraction thus freed of cyclic and acyclic C5 dioletns to more intense second polymerization than said thermal soaking to form stable polymers of remaining cyclic and acyclic diolens, and dstilling benzene from resulting stable polymers of said second polymerization.

2. In a process of separating C5 to Cs cyclic and acyclic diolens from a C5-Ce zich hydrocarbon mixture containing said dioleiins with mainly C5 to Cs monoolens and benzene, the improvement which comprises selectively dimerizing C5 and Ca cyclic diolens in said mixture by thermally soaking said mixture in liquid phase at a temperature of about 200 to 220 F., then separating the remaining unreacted dioletins, mono-olefins and benzene components of said mixture as a distillate from the dimerized cyclic diolefns, fractionally dstilling from said distillate C5 acyclic dioletns to obtain a residual fraction containing C5 acyclic diolctins, mono-olefns and benzene, polymerizing principally the diolens in said residual fraction freed of the dirnerized cyclic dioletins and of C5 acyclic diolefins to stable polymers which are more heat stable than the dimerized cyclic diolens, and dstilling from the said residual fraction, containing the stable polymers, the benzene with the mono-olefins left unreacted.

3. In a process of separating C5 to Cs cyclic and acyclic dioleiins from a C5Ce hydrocarbon rich mixture containing said diolefins with C5 to C5 mono-oleins and aromatic hydrocarbons, the process which comprises first selectively dimerizing C5 and Cs cyclic dioleiins in the C5 to Cs rich mixture by mild thermal dimerization, then separating as a distillate the remaining unreacted Cs-Cs dioletins, mono-olefins and aromatic hydrocarbons from the resulting dimerized cyclic dioleiins in a fractional distillation zone in which temperatures are prevented from exceeding 280 F. to avoid undesired depolymerization of the dimers and undesired polymerization of acyclic diolens, subsequently passing said distillate from the first fractional distillation zone into a second fractional distillation Zone, dstilling in said second fractional distillation zone C5 acyclic diolel'ins to yield a bottoms Cs rich fraction containing benzene, monoolefins, and acyclic diolelins which form polymers when thermally polymerized at temperatures above 220 F., said bottoms Cs-rich fraction being thus substantially freed of C5 diolefins polymerizing principally the Ce diolens in said bottoms fraction removed from second fractional distillation zone to form heat stable polymers therefrom, then dstilling the Ce mono-olens and ben- 6 zene from vthe said thermally stable polymers of the Cs acyclic dioletins. l

V4. In the process of recovering dioleinic and aromatic hydrocarbon products of value from a cracked petroleum, the steps which comprise treating cracked naphtha hydrocarbons in separate streams: l) a C5-Ce rich stream, (2) a C'z-I- rich stream, and 3) a Ca+ rich stream; thermally soaking the C5 rich stream (1) at mild dimerizing temperatures in the range of 200-'220 F. to dimerize Cs-Cs cyclodienes therein, and separating a remaining C5-Cs rich distillate from the resulting dimers; fractionally dstilling from the C'z-lrich stream (2) a narrow benzene-rich distillate fraction boiling in the range of 149 185 F., dstilling from the Cs+ rich stream (3) a lightest C7 rich distillate; fractionally dstilling from said C5-Cs rich distillate from stream (l) after separating the dimers of Cs-Ce cyclodienes its VC5 hydrocarbon components boiling up to F. to obtain a residual fraction rich in Cs and C7 hydrocarbons; combining said Cta-C7 rich residual fraction from stream (1) with the benzene rich intermediate distillate fraction of stream (2) and the lightest C7 distillate fraction of stream (3); subjecting said combined fractions to temperature in the range of 220 F.440 F. until substantially all cyclodiene components and open chain diolens of this fraction undergo polymerization; then fractionally dstilling unpolymerized hydrocarbon components of the thus treated combined fractions to distill benzene and toluene away from a residual polymer product.

5. In a process of separating C5 diolens and Ce-C'z aromatic hydrocarbons from a cracked petroleum naphtha, the steps which comprise treating the cracked petroleum naphtha in at least two separate streams: (l) a Cs-Cs zich stream and (2) a C7 rich stream; thermally soaking the Cs-Cs rich stream at mild dimerizing temperatures in the range of 200-220 F. to dimerize C5-C5 cyclodienes therein; separating the remaining unreacted hydrocarbons of the Cs-Cs rich stream (1) from the resulting dimers by distillation therefrom; then fractionally dstilling from the unreacted hydrocarbons of the C5-Cs rich stream hydrocarbon components boiling up to 140 F. to obtain a residual Cs-Cv fraction rich in benzene; fractionally dstilling from the Cfr-|- rich stream (2) a narrow benzene-rich distillate fraction boiling in the range of 149185 F.; combining the residual Css-C1 rich stream fraction free of components which boil up to 140 F. and free of the cyclodiene dimers with said benzene-rich distillate fraction from the Cf/-lrich stream (2); passing said combined fractions rich in benzene into a polymerization zone; maintaining said combined fractions rich in benzene at temperatures in the range of 220 F.400 F. until substantially all Cs-C'z diolens in said combined fractions undergo polymerization; then passing a resulting hydrocarbon mixture rich in benzene and polymers formed from the polymerization zone into a fractional distillation zone; and dstilling benzene with close-boiling hydrocarbons from the polymers in said fractional distillation zone.

6. In a process of recovering diolenic and aromatic products from a vapor-phase cracked petroleum naphtha, the steps which comprise separating the cracked petroleum naphtha into three separate streams: (l) a Cs-Ce rich hydrocarbon stream containing isoprene, cyclopentadiene, benzene and methyl cyclopentadiene; (2) a C'i-lrich stream and (3) a Cs{- rich stream; thermally soaking the Ca rich stream at mild dimerizing tempera tures in a range of 200-220 F. to dimerize C5-C5 cyclodienes; fractionally dstilling from unreacted hydrocar- .bons of the C5 rich stream hydrocarbon components boiling up to 140 F. to obtain a residual fraction rich in benzene; fractionally dstilling from the C7 rich stream 2) a narrow benzene-rich distillate fraction boiling in the range of 149 F. to 185 F.; dstilling from the Ca+ rich stream a narrow toluene-rich distillate fraction boiling in the range of l200-240 F.; combining said fractions rich References Cited in the tile of this patent UNITED STATES PATENTS Souders etal. Ian. 2, 1945 Borden May 8, 1945 Latchum Jan. 21, 1947 Shepardson May 25, 1948 FOREIGN PATENTS France Oct. 23, 1950 

1. IN A PROCESS OF SEPARATING C5 AND C6 CYCLIC DIOLEFINS, C5 ACYCLIC DIOLEFINS, BENZENE AND HEAT STABLE POLYMERS OF DIOLEFINS FROM VAPOR-PHASE CARACKED NAPHTHA FRACTIONS CONTAINING C5 TO C7+ CYCLIC AND ACYCLIC DIOLEFINS WITH BENEZE, THE STEPS OF THERMALLY SOAKING A C5-C6 RICH FRACTION TO DIMERIZE C5 AND C6 CYCLIC DIOLEFINS THEREIN, DISTILLING REMAINING UNREACTED C5 AND C6 HYDROCARBONS FROM THE DIMERIZED CYCLIC DIOLEFINS, SEPARATING C5 ACYCLIC DIOLEFINS FROM THE RESULTING C5-C6 RICH DISTILLATE WHICH 